With reference to gas turbine members, engine members for aircraft, chemical plant materials, engine members for automobile such as turbocharger rotors, and high temperature furnace materials etc., the strength is needed under a high temperature environment and an excellent oxidation resistance is sometimes required. For that reason, a Ni-base alloy and Co-base alloy have been used for such a high-temperature application. For example, as a typical heat-resistant material such as a turbine blade, a Ni-base superalloy which is strengthened by the formation of γ′ phase having an L12 structure: Ni3(Al,Ti) is listed. It is preferable that the γ′ phase is used to highly strengthen heat-resistant materials because it has an inverse temperature dependence in which the strength becomes higher with rising temperature.
In the high-temperature application where the corrosion resistance and ductility are required, a commonly used alloy is the Co-base alloy rather than the Ni-base alloy. The Co-base alloy is highly strengthened with M23C6 or MC type carbide. Co3Ti and Co3Ta etc. which have the same L12-type structure as the crystal structure of the γ′ phase of the Ni-base alloy have been reported as strengthening phases. However, Co3Ti has a low melting point and Co3Ta has a low stability at high temperature. Thus, in the case of using materials made with Co3Ti and Co3Ta as strengthening phases, the upper limit of the operating temperature is only about 750° C. even when alloy elements are added. A process including steps of: adding Ni, Al, and Ti etc., precipitating, and strengthening with the γ′ phase [Ni2(Al,Ti)] has been reported in Japanese Patent Application Laid-Open (JP-A) No. 59-129746, however, a significant strengthening equal to that of the Ni-base alloy has not been obtained. A process for precipitating and strengthening by using Co3AlC phase having an E21-type intermetallic compound, which has the crystal structure similar to the γ′ phase (JP-A No. 10-102175) has also been examined. However, it has not yet been put to practical use.